Wave-type pressure compensating bases for polymeric containers

ABSTRACT

A plastic container having a sidewall defining a chamber and having a first end and a second end and an opening at the first end into the chamber. A base of the container extends from the sidewall and closes the second end, the base having an outer perimeter portion defining a support structure, an axially inwardly extending perimeter wall spaced radially inwardly from the support structure forming an angle with a horizontal line of greater than about 80°, a centrally disposed pushup section in the shape of an axially inwardly extending truncated cone, and a toroidal-shaped channel circumscribing and connecting the perimeter wall to the pushup section. The toroidal-shaped channel has a surface that is asymmetrical about a central axis of the container when the container is under static pressure conditions.

RELATED APPLICATION

The present application claims priority as a divisional of “parent” U.S.patent application Ser. No. 12/709,302, which will issue as U.S. Pat.No. 8,444,002 on May 21, 2013. The parent application was filed onbehalf of the inventors and was assigned to the assignee of the presentapplication, and is incorporated in the present application byreference.

BACKGROUND OF THE INVENTION

1. Technical Field

This invention relates to pressure compensating bases for polymericcontainers used in hot fill, pasteurization, and retort applications.

2. Background Art

Blow molding processes for forming polymeric containers are well knownin the art. Blown polymeric containers have replaced metal and glasscontainers in numerous food storage applications such as carbonated softdrinks and lower temperature filled food products such as peanut butterand mayonnaise. However, certain prior art containers such aspolyethylene terephthalate (“PET”) containers have not replaced metaland glass containers for product storage and processing applicationswhere the container is filled or heated to temperatures above 97° C.(207° F.) as such containers experience significant shrinkagedeformation rendering the container unusable.

Additional in-roads into the replacement of glass are desired in foodprocessing applications such as low-temperature pasteurization,high-temperature pasteurization, and retort. Low temperaturepasteurization includes the pasteurization of liquid products such asbeer and tea. High temperature pasteurization processes are for solidfood products such as pickles that have slower heat transfer rates andrequire temperatures in excess of 100° C. (212° F.). Retort processesare for pasteurizing low acid products and require temperatures from100° C. to 130° C. (212° F. to 266° F.) and pressures sufficient tomaintain water in a liquid state.

In numerous food storage applications, polymeric containers are filledwith a hot liquid or solid material, the container is capped and thenallowed to cool. To compensate for the change in volume inside thecontainer it is known to provide pressure compensating features invarious locations on the container sidewall including the dome, thebarrel, and the bottom panel. The pressure compensating features move inresponse to pressure changes to decrease or increase the volume asneeded. United States Publication Nos. 2009/0202766 and 2009/0159556 andU.S. Pat. Nos. 7,451,886; 7,150,372; 6,942,116; and 6,595,380 disclose avolume compensating feature on a bottom panel of the container having acentrally disposed, generally inverted, cone shaped, push-up sectionthat extends to an axially inwardly most point when compared to otherportions of the bottom panel. The push up section is connected by agenerally S-shaped panel to a standing ring. The S-shaped panel invertsto compensate for negative pressure in the container. The '556publication further discloses providing a plurality of axially spaced,circumferentially extending grooves on the S-shaped panel that extendthrough the entire thickness of the wall and form ribs on an oppositeside of the groove or a plurality of circumferentially and axiallyspaced dimples. The bottom panels are symmetrically disposed about anaxis of the container.

U.S. Pat. Nos. 6,983,858; 6,857,531; and 5,234,126 disclose a pressurecompensating base for a polymeric container that under static pressurethe bottom panel is convex, or extends axially outwardly, and snapsthrough to a concave configuration, or extends axially inwardly, when aspecific pressure is reached within the container.

United States Patent Application Publication No. 2006/0231985 disclosesa method and apparatus for manufacturing a blow molded container. Aparison is mounted within a mold assembly having two side molds and abase mold. The parison is inflated in contact with surfaces of the moldassembly to form a container with a bottom wall having a moveableregion. The moveable region is downwardly convex with respect to abearing surface and has a centrally disposed dimple. After the inflationstep is complete, a rod mounted within the base mold for reciprocatingtranslational motion along an axis of the container is moved axiallyinwardly so that a rod end engages the dimple of the moveable region toreposition the moveable region axially inwardly to an interior portionof the container with respect to the bearing surface.

United States Patent Publication No. 2008/0047964 discloses a plasticcontainer having an invertible base for pressure compensation. Apressure panel is deeply set into the container and is moveable betweenan outwardly inclined position to an inwardly inclined position toreduce the internal volume of the container and to compensate for vacuumforces created during a hot-fill process. The pressure panel isconnected to the standing ring by an inner wall that is parallel ornearly parallel to a longitudinal axis of the container. To facilitatemovement of the pressure panel between the outwardly inclined positionto the inwardly inclined position, the pressure panel can include ahinge structure that is located between the inner wall and the pressurepanel. The pressure panel can have an initiator portion and a controlportion where the control portion has a steeper angle with respect to astanding plane than the initiator portion. The '964 application furtherdiscloses a pressure panel divided into fluted regions to create regionsof lesser and greater angular inclination.

To overcome the shortcomings of known containers, a new plasticcontainer having pressure compensating features is provided. Thecontainer may have a pressure compensating base capable of progressivelyyielding under pressure. The pressure compensating base of the presentinvention will allow for all other surfaces of the container to be freeof pressure compensating features. These and other aspects andattributes of the present invention will be discussed with reference tothe following drawings and accompanying specification.

SUMMARY OF THE INVENTION

The present invention provides a plastic container having a sidewalldefining a chamber and having a first end and a second end and anopening at the first end into the chamber. A base of the containerextends from the sidewall and closes the second end, the base having anouter perimeter portion defining a support structure, an axiallyinwardly extending perimeter wall spaced radially inwardly from thesupport structure forming an angle with a horizontal line of greaterthan about 80°, a centrally disposed pushup section in the shape of anaxially inwardly extending truncated cone, and a toroidal-shaped channelcircumscribing and connecting the perimeter wall to the pushup section.The toroidal-shaped channel has a surface that is asymmetrical about acentral axis of the container when the container is under staticpressure conditions.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary, but are notrestrictive, of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a jar-type container;

FIG. 2 is a side elevation view showing a preform overlaid onto a moldcavity for a jar-type container;

FIGS. 3-10 show four embodiments of a hinge-type base having a generallyround bottom pressure relief section respectively showing a bottom viewand a side sectional view of each embodiment;

FIGS. 11-14 show two embodiments of a hinge-type base having a generallysquare pressure relief section respectively showing a bottom view and aside sectional view of each embodiment;

FIGS. 15 and 16 show a hinge-type base having a round pressure reliefsection having eight radial hinges and two circumferential hingesrespectively showing a bottom view and a side sectional view;

FIGS. 17-19 show side elevation views of the hinge base on the containerof FIG. 5 taken along line 6-6 under various pressure conditionsincluding respectively under vacuum, static pressure and positivepressure;

FIG. 20 is a side elevation view in cross-section of a blow station witha stretch rod partially inserted into a blow mold;

FIG. 21 is a side elevation view in cross-section of the blow stationwith the stretch rod fully inserted into the blow mold and stretching anintermediate container into an overstretched condition;

FIG. 22 is a side elevation view in cross-section of the blow stationshowing the forming of the bottom container with a stretch rod and apushup member;

FIG. 23 is a side elevation view in cross-section of the blow stationhaving a blow mold in an open condition with a two-piece pushup memberin a retracted position;

FIG. 24 is a side elevation view in cross-section of the blow stationwith the blow mold moving to a closed position and a first portion ofthe pushup in a molding position and a second portion in a retractedposition;

FIG. 25 is a side elevation view in cross-section of the blow stationwith the blow mold in a closed position with the first portion and thesecond portion of the pushup in a molding position;

FIG. 26 is a side elevation view of the blow mold moving to an openposition with the first and second portions of the pushup inserted intothe mold cavity;

FIG. 27 is a side elevation view of the blow mold in an open positionwith the first portion of the pushup inserted into the mold cavity andthe second portion in a retracted position;

FIG. 28 is a side elevation view of the blow mold moving to an openposition with the first and second portions of the pushup in a retractedposition;

FIGS. 29-34 are side sectional views of a base of a container having aprogressive-type or wave-type release rate;

FIGS. 35 and 36 respectively are a bottom view and a side sectional viewof a wave or progressive base with a generally circular pressure reliefsection within a generally square standing ring;

FIGS. 37 and 38 respectively are a bottom view and a side sectional viewof a wave or progressive base with a generally square pressure reliefsection within a generally square standing ring;

FIGS. 39-42 show side elevation views of a representative wave base on acontainer respectively under various pressure conditions including undervacuum with the base fully inverted, under vacuum with the basepartially inverted, under static pressure conditions and under positivepressure; and

FIG. 43 shows a plot of a deflection curve for a container having thepressure compensating panel shown in FIGS. 5 and 17-19 when thecontainer is filled with boiling water and capped, with the distance ofdeflection of the pressure panel measured from a static position plottedin inches on the y-axis and the amount of internal pressure of thecontainer plotted on the x-axis in millibars.

DETAILED DESCRIPTION OF THE INVENTION

While this invention is susceptible of embodiment in many differentforms, there are shown in the drawings, and will be described herein indetail, specific embodiments thereof with the understanding that thepresent disclosure is to be considered as an exemplification of theprinciples of the invention and is not intended to limit the inventionto the specific embodiments illustrated.

The present invention provides pressure compensating bases for polymericcontainers and more preferably for containers of a crystallizablepolymer having enhanced thermal properties while still providing acontainer with high clarity. Suitable crystallizable polymers include,for example, homopolymers of poly (ethylene terephthalate) and phthalicbased copolymers (“PET”), polyolefins, polypropylene and polyethylene.Suitable polyolefins include homopolymers and copolymers of olefins withcomonomers of olefins, ethers, esters, amides and others well known tothose skilled in the art. Suitable polyethylenes include homopolymersand copolymers of ethylene and also include high, medium and low densitypolyethylenes.

In a preferred form of the invention, the containers will be fabricatedfrom PET resin having an intrinsic viscosity from 0.72 to about 0.86.Suitable PET resins include bottle grade PET resins including PARASTARresins sold by the Eastman Chemical Company, PET resins sold by Wellman,Inc., and CLEAR TUF resins sold by M&G Polymers. The crystallizablepolymer containers of the present invention can have any geometry,shape, or size without departing from the present invention and includecontainers that are round, oval, polygonal, and irregular. Suitablecontainers can be a jar-type, can-type, carafe, wide mouth, and anyother type of container known to those of ordinary skill in the art.Suitable features of the containers can include pressure absorbingfeatures, grip enhancing features, shoulders, bumpers, finishes, chimes,standing rings, necks, and others known to those of ordinary skill inthe art.

FIG. 1 shows one container of the present invention in the form of a can1, having a generally cylindrical sidewall 2, a pressure compensatingbase 4, and an open top 6 circumscribed by a flange section 8. FIG. 2shows a mold cavity 10 and a preform 12 for forming a jar-type containerhaving a conical top section 14, a finish section 16, a shoulder section18, a first bumper section 20, a sidewall or barrel section 22, a bottomsection 24, and a second bumper section 26. The pressure compensatingbase 4 has a standing ring 27 forming a support structure and having afirst outer diameter (FIG. 4). An upstanding wall 29 extends axiallyinwardly and forms an angle with respect to the horizontal support lineof greater than about 80° and more preferably from about 80° to about90°. Spanning a top end 54 of the upstanding wall 29 is a pressurecompensating panel 28 having a second diameter (FIGS. 4 and 17) fromabout 70% to about 95% of the standing ring first diameter, morepreferably from about 80% to about 95% and most preferably from about85% to about 93%. Containers of the present invention include thosevolumes that are commonly used in the food industry and chemicalindustry and can include, for example, from 4 oz. to 128 oz. However, itshould be understood the present invention should not be limited to thisvolume range.

In a preferred form of the invention, the containers will be formed onan integrated platform with a blow mold station. What is meant by anintegrated platform is that the preform 12 is formed in line with theblow mold cavities. Thus, the preform 12 does not have to be reheated toa preferred orientation temperature as is required of non-integratedplatforms. Further, in non-integrated platforms, preforms may increasein moisture content over time which is undesirable. Accordingly, thepreform of an integrated system will have a single heat history unlike apreform that is formed, cooled, and then reheated to the desiredorientation temperature and, therefore, has multiple heat histories. Ina preferred form of the invention, the preform 12 will have a moisturecontent of less than about 30 ppm.

In a preferred form of the invention of FIG. 2, the single-heat historypreform 12 will be disposed within a blow mold cavity 10 of a blowstation having a temperature higher than the glass transitiontemperature (“Tg”), and more preferably within the range of 73° C. to250° C. (163° F. to 482° F.), more preferably 150° C.-240° C. (302° F.to 464° F.), more preferably 30° C.-230° C. (86° F. to 446° F.), andmost preferably from 30° C.-200° C. (86° F. to 392° F.) and any range orcombination of ranges therein. The container will remain in the moldfrom about two seconds to about twenty seconds, more preferably fromabout two seconds to fifteen seconds, more preferably from about twoseconds to about twelve seconds, more preferably from about four secondsto twelve seconds, and most preferably from about six seconds to abouttwelve seconds. A more detailed description of the preferred method offorming a PET container with enhanced thermal stability is set forthbelow with reference to FIGS. 23-28 and in co-pending and commonlyassigned U.S. patent application Ser. No. 12/564,845, now allowed, whichis incorporated in its entirety herein by reference and made a parthereof.

In a preferred form of the invention, the container will have sidewallsof varying thicknesses and more preferably the thickness of the pressurecompensating panel 28 will be thinner than the thickness of the sidewall2 (FIGS. 1) and 22 (FIG. 2). In one preferred form of the invention thethickness of the pressure compensating panel 28 will be from about 30%to about 60% thinner than the thickness of the sidewalls 2 and 22. Wallthicknesses in the base area can vary but for food containerapplications the thickness of the wall in the base area will be fromabout 0.012″ (0.030 cm) to about 0.016″ (0.040 cm).

In a preferred form of the invention, the pressure compensating base 4will be capable of progressively yielding under pressure. FIGS. 3-14show various embodiments of a pressure compensating base 4 each havingpanels divided by hinges. Accordingly, this type of pressurecompensating base will sometimes be referred to as a hinged-type base30. FIGS. 29-32 show various embodiments of a pressure compensating base4 having an asymmetric structure that progressively yields. This type ofbase may sometimes be referred to as a wave base. In preferred forms ofthe invention, both the hinged-type base and the wave-type base willcompensate for pressure differences so that the barrel section has acontinuous surface uninterrupted by pressure compensating structuressuch as indentations, ribs, or other pressure compensating features. Inanother preferred form of the invention, the pressure compensating bases4 of the present invention will allow for all other surfaces of thecontainer to be free of pressure compensating features.

In a preferred form of the invention, the hinged-type base 30 will haveat least two panels 32 divided by a groove or hinge 34 and a centrallypositioned push up section 36. The present invention contemplates havingany number of grooves or hinges 34 including, for example, from 1 grooveor hinge to 100 grooves or hinges. The grooves or hinges 34 can extendalong a line in any direction including axially, circumferentially, oralong a chord (“chordally”) and any combinations of these. Also, thegroove 34 can extend axially inwardly of the pressure compensating base4 or axially outwardly of the pressure compensating base 4. A groove 34is shown, in a preferred form, as a groove through the partial thicknessof a wall of the base 4, with no interruption of an opposing wallsurface, and provides a line along which the two panels 32 can flex. Itis contemplated that the groove 34 could also extend through the entirethickness of the panel 32 and form an upstanding rib on an opposingsurface. The present invention contemplates having a base 30 having allaxially inwardly extending grooves 34, a side with all axially outwardlyextending grooves 34, or a side with a combination of axially inwardlyand axially outwardly extending grooves 34.

FIGS. 3, 4 and FIGS. 11, 12 respectively show a hinged-type round bottomand square bottom container each having eight circumferentially spacedand radially extending hinges 34 and eight panels 32. In a preferredform of the invention, the radial hinges 34 will be substantiallyequally spaced from one another and in the case of eight hinges 34 eachhinge 34 is spaced from adjacent hinges 34 by 40 degrees. The axiallyextending hinges 34, in a preferred form of the invention, will notextend beyond the diameter of the pressure compensating panel 28, andmore preferably will initiate proximate the upstanding wall 29, withouttouching the upstanding wall 29, and terminate short of the pushupsection 36. The length of the grooves 34 will be from about 85% to about100% of the first diameter of the standing ring 27. The grooves 34 willpreferably have a width from about 0.030 inches (0.076 cm) to about0.080 inches (0.203 cm), more preferably from about 0.035 inches (0.089cm) to about 0.065 inches (0.165 cm), and most preferably from 0.035inches (0.089 cm) to about 0.045 inches (0.114 cm). The grooves 34 willalso have a depth of from about 0.045 inches (0.114 cm) to about 0.120inches (0.305 cm), more preferably from about 0.050 inches (0.127 cm) toabout 0.100 inches (0.254 cm), and most preferably from about 0.055inches (0.139 cm) to about 0.080 inches (0.203 cm).

FIGS. 5, 6 and FIGS. 13, 14 respectively show a hinged-type round bottomand square bottom each having a combination of eight circumferentiallyspaced and radially extending hinges 34 and a circumferentiallyextending hinge 38 that intersects each of the radially extending hingesalong an intermediate portion of the length of the radial hinges. Thecircumferential hinge 38 is concentrically disposed and has a diameterof from about 45% to about 75% of the diameter of the standing ring 27.It is contemplated providing additional circumferential hinges 38radially spaced from one another including two or more circumferentialhinges 38 (FIGS. 15 and 16). FIGS. 7-10 show a similar structure butwith twelve radial hinges instead of eight.

FIGS. 4, 6, 8, 10, 12, and 14 show, in one preferred form of theinvention, when the container is at static pressure, the panels 32 havea curved outer surface 40 tapering axially outwardly from a radialoutward end to a radial inward end. The radial inward end terminatesproximate the push up section 36.

FIGS. 17-19 show the hinged-type base 30 under various pressureconditions within the container. FIG. 43 shows a plot of a deflectioncurve for a container having the pressure compensating panel shown inFIGS. 5 and 17-19 when the container is filled with boiling water andcapped, with the distance of deflection of the pressure panel measuredfrom a static position plotted in inches on the y-axis and the amount ofinternal pressure of the container plotted on the x-axis in millibars.FIG. 17 shows the pressure relief panel fully inverted to compensate fora vacuum or negative pressure within the container. Because the pressurecompensating panel 28 has numerous hinges 34 and panels 32, the panels32 can progressively yield or yield simultaneously depending on thepressure difference between the inside of the container and the outsideof the container. FIGS. 17-19 show end points in the yielding process.When in the static or positive pressure environments (FIGS. 18 and 19),the central portion or pushup section 36 of the panel 32 is below thetop end 54 of the upstanding perimeter wall 29 and, when under vacuumconditions (FIG. 17), the central portion or pushup section 32 is abovethe top end 54 of the upstanding perimeter wall 29.

In a preferred form of the invention, when the container is at staticpressure (FIG. 18), the angle a formed between a horizontal line and abottom surface of a panel 32 will be within the range of 15° to 45°, andmore preferably between 18° to about 35°, and most preferably from about20° to about 33°. Further, in a preferred form of the invention, theangle β between a line 50 representing the average radii of curvature(drawn between the highest point on the panel (axial inward most point)to the lowest point (axial outward most point) will be within the rangeof 5° to about 30°, more preferably from about 10° to 25°, and mostpreferably from about 10° to about 20°.

When the container is under a vacuum (FIG. 17), in a preferred form ofthe invention, the angle β′ will be greater than the angle β by 2° toabout 15° and more preferably from 2° to about 10°. Also, in a preferredform of the invention, the angle β′ will be within the range of 10° toabout 45°, more preferably from about 13° to about 33°, and mostpreferably from about 13° to about 25°.

When the container is under positive pressure (FIG. 19), the angle α′will be from about 20° to about 50°, more preferably from about 23° toabout 45°, and most preferably from about 25° to about 40°. Also, in apreferred form of the invention, the angle β″ will be within the rangeof 15° to 40°, more preferably from about 15° to about 33°, and mostpreferably from about 15° to about 30°.

When the container is under static pressure (FIG. 18), a distance A froma support surface to the central portion or pushup section 36 will beabout 0.180 inches (0.457 cm) to about 0.360 inches (0.914 cm) for acontainer having a standing ring 27 with a diameter of from about 2.500inches (6.350 cm) to about 3.000 inches (7.620 cm). Thus, the ratio ofthe distance A to the standing ring diameter will be from about 7:1 toabout 17:1.

When the container is under a negative pressure (FIGS. 17 and 43), thepressure compensating panel will deflect as shown in FIG. 43.

When the container is under positive pressure (FIG. 19), the distance A″will be from about 0.050 inches (0.127 cm) to about 0.110 inches (0.279cm) for a container having a standing ring 27 with a diameter of 2.678inches (6.802 cm). Thus, the ratio of (A-A″)/standing ring diameter isfrom about 27:1 to about 38:1. Further, the difference between A″ and Ndefines the flex range of the panel and, for a container having astanding ring diameter of 2.678 inches (6.802 cm), the flex range willbe from 0.450 inches (1.143 cm) to about 0.640 inches (1.626 cm) for aratio of flex range to standing ring diameter of from about 4:1 to about6:1.

In one preferred form of the invention, the container will be formed ina blown extrusion process where a preform is inserted into a blow moldand blown into an intermediate container having an axial dimensiongreater than the axial dimension of a finished container and forming thepushup section of the container. FIGS. 20-22 show one preferred blowmold station 70 having a wall 72 defining a cavity having the desiredshape of the intermediate container. A pushup member or cavity insert 76forms a bottom wall of the cavity and is mounted for reciprocatingtranslational movement along an axis of the cavity from a first positionoutward of the cavity (FIGS. 20, 21) to a second position (FIG. 23)axially inward. The pushup member has an outer surface 77 having asurface profile necessary to form the desired pressure compensating basediscussed above with reference to FIGS. 3-19. FIGS. 20-22 also show acarrier 78 for holding a top portion of the preform during conveyance ofthe preform to the blow mold station 70.

FIGS. 20-22 show a stretch rod 80 mounted for reciprocatingtranslational motion along an axis of the cavity. In a first positionshown in FIG. 20, the stretch rod 80 initially contacts a bottom portion82 of the preform. The preform is then blown into contact with an innersurface of the cavity to form the intermediate container 84 having awall 43. The stretch rod 80 is moved to a second position where itstretches the intermediate container 84 in an axial direction beyond thedesired axial dimension of the finished container to define anoverstretched position or overstretched container. The container isoverstretched along an axial direction from about 15 mm to 40 mm, morepreferably from about 20 mm to about 35 mm, and most preferably fromabout 20 mm to about 30 mm greater than the axial dimension of thefinished container. FIG. 22 shows the pushup member or insert 76advancing axially inwardly to stretch the overstretched intermediatecontainer into a smaller axial dimension than when overstretched.

FIGS. 23-28 show a second embodiment of a blow station, which is thesame in all respects to the blow station discussed with respect to FIGS.20-22, with the exception of having a two-piece pushup assembly 76′having a first section 98 and a second section 100 coaxially disposedabout the first section 98. FIGS. 23-25 show three sequential steps inclosing a mold and FIGS. 26-28 show three sequential steps in opening amold.

FIG. 23 shows a blow mold having first and second portions 101 a,b,separated from one another forming a gap 102. The first and secondportions 101 a,b, are mounted for reciprocal translational movement froman open position to a closed position. When in the open position shownin FIG. 23, a finished container (not shown) is removed from the moldand a new preform is inserted. When in the closed position, the processof blow molding the container occurs.

The first and second pushup sections 98 and 100 are also mounted forreciprocating translational motion from retracted positions to moldingpositions independent of one another. In a preferred form of theinvention, the pushup sections will move along a line that is transverseto the line upon which the first and second mold portions 101 a,b moveand even more preferably in a line essentially perpendicular thereto. Inanother preferred form of the invention, both the first and secondpushup sections 98 and 100 are capable of being independently movedaxially away from the mold and independently into the mold. That is, thefirst section 98 and the second section 100 are mounted forreciprocating translational motion between positions inside the moldcavity and outside the mold cavity independent of one another. In apreferred form of the invention, the first and second sections 98 and100 are capable of being independently moved axially into the moldcavity from a retracted position to a molding position. FIG. 23 showsthe first and second sections 98 and 100 in a retracted position, FIG.24 shows second section 100 in a molding position with the first section98 in the retracted position and FIG. 25 shows both the first and secondsections 98 and 100 in the molding position.

The first section 98 has a surface 99 for forming one annular section ofthe bottom of the container and the second section 100 has a surface 101for forming a second annular section of the bottom and the secondsection is preferably concentrically disposed about the first section.More preferably, the first section 98 has a surface 99 for formingportions of the bottom panel axially inwardly of the annular upstandingwall 29 including features discussed above with reference to FIGS. 1-19.The second section 100 forms the portions of the bottom panel from thestanding ring 27 axially inwardly to and including the upstanding wall29.

The present invention provides a three-step method for closing (FIGS.23-25) and opening (FIGS. 26-28) the mold. FIG. 23 shows the twoportions of the mold 101 a,b in a first open position and the twosections of the pushup 98 and 100 in their retracted positions. FIG. 24shows the two portions of the mold 101 a,b after moving in the directionof the arrows to a second closed position, the first section of thepushup 98 having moved axially inwardly into the molding position, andthe second pushup section 100 remaining in its retracted position. Inthe second closed position, the standing ring 27 and upstanding wall 29are formed. FIG. 25 shows the two portions of the mold 101 a,b in athird, closed position having the two sections of the pushup 98 and 100in their molding positions. In the third, closed position, the flexiblepanel wall is formed and the finished container is formed.

FIG. 26 shows the two portions of the mold 101 a,b have moved to an openposition and the two sections of the pushup 98 and 100 are in theirmolding positions. The finished container is exposed to ambientconditions and begins to cool. FIG. 27 shows the next step: while thetwo mold portions 101 a,b are in an open position, the first section 98of the pushup is moved to its retracted position while the secondsection 100 remains in its molding position and continues to providesupport to the finished container. FIG. 28 shows the two mold portions101 a,b in the open position and both of the two sections of the pushup98 and 100 are in their retracted positions. Thus, the position of theblow station shown in FIG. 28 is the same position as shown in FIG. 23.It is in this position when the finished container is removed from themold and a new preform is inserted and the process is repeated.

FIGS. 29-34 show six embodiments of the wave-type bases 110 having theupstanding wall 29, a contact ring 114, and an axially inwardlyextending pressure relief section 116 spaced radially inwardly from thecontact ring 114. The pressure relief section 116 is asymmetrical incross sectional dimension and under static conditions so that oneportion of the pressure relief section 116 yields under a first pressureand a second portion of the pressure relief section 116 yields under asecond pressure different from the first pressure (see FIGS. 39-42). Inone preferred form of the invention, the pressure relief section 116 hasa first generally vertically extending wall 118, a first radiallyinwardly extending rounded transition 120, a second generally verticallyextending wall 122, a second radially inwardly extending roundedtransition 124, a first transition panel 126, a second transition panel127, and a central push up 128. The first and second transition panels126, 127 define a generally toroidal-shaped channel circumscribing thecentral pushup 128. The second rounded transition 124 has portionsspaced apart by 180°. The radius of curvature of the first portion isdifferent from the radius of curvature at the second portion to definean asymmetric pressure relief panel. Thus, there will be a radii ofcurvature gradient between a maximum and a minimum. In one preferredform of the invention, the maximum and minimum radii of curvature willbe separated by 120° and in another form of the invention by 180°. FIGS.29-34 show the 180° embodiment. In the embodiment where the maximum andminimum are separated by 120° there will be one 120° segment going fromthe minimum curvature to the maximum curvature, a second 120° segmentgoing from the maximum curvature to the minimum curvature, and finally athird 120° segment where there is no change in the radius of curvature.The first rounded transition 120 has opposed rounded sections 130, 132and a straight section 134 therebetween.

Due to the radii of curvature gradients in the 180° embodiment, thefirst and second transition panels 126 and 127 have geometries thatdiffer in at least one dimension to render the shape of the pressurerelief section 116 asymmetrical. In the 120° embodiment, there would bethree segments or panels of differing shapes with a first panel havingan upwardly sloping surface from the minimum to the maximum, a secondpanel with a downwardly sloping surface from the maximum to the minimum,and a third panel that is essentially flat with a constant radius ofcurvature over the entire surface. FIGS. 29, 31 have generally concaveor semi-circular shaped transition panels 126 and 127 with the radius ofcurvature of the panels being different from one another. Moreparticularly, in FIGS. 29 and 31 the second transition panel 127 has anaxially deeper shape than the first transition panel 126, and,therefore, presents greater resistance to yielding under negativepressure within the container and less resistance to yielding underpositive pressure within the container.

In another preferred form of the invention, the pressure relief section116 is asymmetric under static conditions due to having differences inthe slope of the section from the second transition at variouscircumferentially spaced points along a top of the perimeter wall todefine a slope angle gradient between a maximum and a minimum. In FIGS.30 and 32, the transition panels 126, 127 have a first leg 136 and asecond leg 138. The first leg 136 is generally downwardly sloping andradially inwardly extending along a straight line and the second leg 138is rounded. The downwardly sloping line forms an angle α with ahorizontal line (radial) of from about 5 degrees to about 45 degrees andmore preferably from about 10 degrees to about 30 degrees. Asymmetryresults from differing a angles of the first leg 136 of each of thefirst and second transition panels 126 and 127.

In a preferred form of the invention, the difference in the α anglesbetween the first and second transition panels 126, 127 will be fromabout 3 degrees to about 30 degrees and more preferably from about 5degrees to about 20 degrees. The α angles of the first and secondtransition panels 126, 127 of FIG. 27 are 15° and 27°.

FIGS. 35 and 36 show the pressure relief section 116 has a generallyround shape and FIGS. 37 and 38 show the pressure relief section 116 hasa generally square shape. The contact ring 114 in FIGS. 35-38 isgenerally square shaped with rounded vertices. It should be understood,however, that it is contemplated both the pressure relief section 116and the contact ring 114 could have other shapes such as circular, oval,polygonal, and irregular without departing from the scope of the presentinvention.

In a preferred form of the present invention, the push up 128 isgenerally a truncated cone having a generally vertically extending wall142 tapering axially inwardly from a first point to a second pointaxially inwardly from the first and having a generally flat top wall144. In a preferred form of the invention, the top wall 144 of the pushup 128 will extend axially inwardly beyond the second transition panel126 by a distance 146 within the range of from about 0.625 inches (1.587cm) to about 1.125 inches (2.857 cm).

FIGS. 39-42 show a representative wave-type base 110 in various pressureconditions. FIG. 39 shows the first and second transition panels 126 and127 fully inverted in response to a vacuum or negative pressure withinthe container. FIG. 40 shows the first transition panel 126 beginning toinvert causing the upper surface of the pushup 128 to form an angle βwith an axis 147. FIG. 41 shows the base 110 when the pressure in thecontainer is at atmospheric pressure. FIG. 42 shows the base 110 flexedaxially outwardly in response to a positive pressure within thecontainer.

For containers in need of enhanced gas or water vapor transmissionrates, a barrier layer or coating can be used provided the material hasno adverse effects on the intended use of the container. One suitablecoating material is a silicon oxygen coating (SiOx) deposited on asurface of the container, preferably on an interior surface, usingtechniques such as plasma deposition. Other suitable barrier materialsand coatings are well known to those skilled in the art.

The present invention provides a method for forming a polymericcontainer including the steps of: (1) providing a blow mold having achamber and an opening into the chamber at one end, the blow mold beingmoveable between an open position and a closed position, a pushup memberis positioned in the opening to close the chamber, the pushup memberhaving a surface extending into the chamber for defining a bottom wallof the container; (2) inserting a preform within the blow mold; and (3)blowing the preform against the chamber to form a container having abase, the base having an outer perimeter portion defining a supportstructure, an axially inwardly extending perimeter wall spaced radiallyinwardly from the support structure foaming an angle with a horizontalline of greater than about 80°, and a pressure compensating panelclosing an end of the perimeter wall, the pressure compensating panelbeing moveable along an axis of the container from a first positionwhere a central portion of the panel is below a top portion of theperimeter wall to a second position where the central portion is abovethe top portion of the perimeter wall to change the volume of thecontainer, and a plurality of circumferentially spaced radial grooves onthe panel.

The present invention also provides a method for releasing a blow moldedcontainer from an extrusion blow mold including the steps of: (1)providing a blow mold having a chamber and an opening into the chamberat one end, the blow mold being moveable between an open position and aclosed position and having a container positioned in the chamber; (2)providing a two-piece pushup assembly positioned in the opening to forma bottom wall of the blow mold and having a first portion and a secondportion; (3) moving the blow mold to the open position; (4) withdrawingthe first portion away from the mold while the second portion remains inthe mold; (5) withdrawing the second portion away from the mold; and (6)removing the container from the chamber.

From the foregoing, it will be observed that numerous variations andmodifications may be effected without departing from the spirit andscope of the invention. It is to be understood that no limitation withrespect to the specific apparatus illustrated herein is intended orshould be inferred. It is, of course, intended to cover by the appendedclaims all such modifications as fall within the scope of the claims.

We claim:
 1. A plastic container comprising: a sidewall defining achamber and having a first end and a second end and an opening at thefirst end into the chamber; and a base extending from the sidewall andclosing the second end, the base having an outer perimeter portiondefining a support structure, an axially inwardly extending perimeterwall spaced radially inwardly from the support structure forming anangle with a horizontal line of greater than about 80°, a centrallydisposed pushup section in the shape of an axially inwardly extendingtruncated cone, and a toroidal-shaped channel circumscribing andconnecting the perimeter wall to the pushup section, the toroidal-shapedchannel having a surface that is asymmetrical about a central axis ofthe container when the container is under static pressure conditions. 2.The container of claim 1 wherein the surface of the toroidal-shapedchannel has a rounded transition having a first radius of curvature at afirst point and a second radius of curvature at a second pointcircumferentially spaced from the first point, the first radius ofcurvature being different from the second radius of curvature to definea radii of curvature gradient.
 3. The container of claim 2 wherein thefirst point is spaced from about 120° to about 180°.
 4. The container ofclaim 1 wherein the surface of the toroidal-shaped channel has a firstleg and a second leg circumferentially spaced from the first leg, thefirst leg forming a first angle with a horizontal line and the secondleg forming a second angle with a horizontal line and the first angle isdifferent from the second angle defining an angle gradient therebetween.5. The container of claim 4 wherein the maximum difference between thefirst angle and the second angle is less than about 30°.
 6. Thecontainer of claim 1 wherein the truncated cone has a top surface thatforms varying angles with a horizontal support surface when thecontainer collapses.
 7. A plastic container comprising: a sidewalldefining a chamber and having a first end and a second end and anopening at the first end into the chamber; and a base extending from thesidewall and closing the second end, the base having an upstanding wall,a contact ring, and an axially inwardly extending pressure reliefsection spaced radially inwardly from the contact ring, wherein thepressure relief section is asymmetrical in cross sectional dimension andunder static conditions so that one portion of the pressure reliefsection yields under a first pressure and a second portion of thepressure relief section yields under a second pressure different fromthe first pressure.
 8. The container of claim 7 wherein the pressurerelief section has a first generally vertically extending wall, a firstradially inwardly extending rounded transition, a second generallyvertically extending wall, a second radially inwardly extending roundedtransition, a first transition panel, a second transition panel, and acentral pushup, and wherein the first and second transition panelsdefine a generally toroidal-shaped channel circumscribing the centralpushup.
 9. The container of claim 8 wherein one of the roundedtransitions has a first radius of curvature at a first point and asecond radius of curvature at a second point circumferentially spacedfrom the first point, the first radius of curvature being different fromthe second radius of curvature to define a radii of curvature gradientbetween a maximum and a minimum.
 10. The container of claim 9 whereinthe maximum and minimum radii of curvature are separated by about 120°.11. The container of claim 9 wherein the maximum and minimum radii ofcurvature are separated by about 180°.
 12. The container of claim 8wherein each of the transition panels has a first leg and a second leg,with the first leg sloping generally downwardly and extending radiallyinwardly along a straight line and the second leg being rounded, thedownwardly sloping line forming an angle with a horizontal line of fromabout 5° to about 45°.
 13. The container of claim 12 wherein the anglesof the first leg of each of the first and second transition panelsdiffer, creating the asymmetry of the pressure relief section.
 14. Thecontainer of claim 13 wherein the maximum difference between the anglesof the first leg of each of the first and second transition panels isless than about 30°.
 15. The container of claim 7 wherein the pressurerelief section has a generally round shape.
 16. The container of claim 7wherein the pressure relief section has a generally square shape. 17.The container of claim 7 wherein the contact ring is generally squareshaped with rounded vertices.
 18. The container of claim 8 wherein thepushup is a generally truncated cone having a generally verticallyextending wall tapering axially inwardly from a first point to a secondpoint axially inwardly from the first point and having a generally flattop wall.
 19. The container of claim 18 wherein the top wall of thepushup extends axially inwardly beyond the second transition panel by adistance within the range of from about 0.625 inches to about 1.125inches.
 20. A plastic container comprising: a sidewall defining achamber and having a first end and a second end and an opening at thefirst end into the chamber; and a base extending from the sidewall andclosing the second end, the base having an upstanding wall, a contactring, and an axially inwardly extending pressure relief section spacedradially inwardly from the contact ring, wherein the pressure reliefsection is asymmetrical in cross sectional dimension and under staticconditions so that one portion of the pressure relief section yieldsunder a first pressure and a second portion of the pressure reliefsection yields under a second pressure different from the firstpressure, wherein the pressure relief section has a first generallyvertically extending wall, a first radially inwardly extending roundedtransition, a second generally vertically extending wall, a secondradially inwardly extending rounded transition, a first transitionpanel, a second transition panel, and a central pushup forming agenerally truncated cone having a generally vertically extending walltapering axially inwardly from a first point to a second point axiallyinwardly from the first point and having a generally flat top wall,wherein the first and second transition panels define a generallytoroidal-shaped channel circumscribing the central pushup, and whereinone of the rounded transitions has a first radius of curvature at afirst point and a second radius of curvature at a second pointcircumferentially spaced from the first point, the first radius ofcurvature being different from the second radius of curvature to definea radii of curvature gradient between a maximum and a minimum.